In a case that could chill free speech online, a San Francisco chiropractor has sued a local artist over negative reviews published on Yelp, the popular Web site that rates businesses.

Christopher Norberg, 26, of San Francisco posted the first review in November 2007 after visiting Steven Biegel at the Advanced Chiropractic Center on Valencia Street. In the six-paragraph write-up, Norberg criticized Biegel's billing practices and said the chiropractor was being dishonest with insurance companies.

When the chiropractor complained about the review, Norberg replaced it with a new entry a few weeks later that read in part, "I think that he is trying to scare me into removing a negative post (that might explain why he has only positive ones). I believe that he has been harassing me into shutting up, and I feel as a consumer I have a voice and that I can use it on forums made for sharing it, especially when I feel that the experience was unsatisfactory."

Biegel said both reviews were malicious and in February sued Norberg for libel and invasion of privacy. If the case isn't settled, it will go to trial in March in San Francisco Superior Court.

"I'm not looking for my 15 minutes of fame," Biegel said Wednesday. "This suit was filed after a year of trying to resolve this. I am a proponent of free speech, but at the same time, individuals have a responsibility when they publish something as to the accuracy of it."

The case raises questions about whether people can use the Internet to express negative feelings about others and also about the long-term viability of businesses like Yelp that publish third-party reviews, even though Yelp - under the federal Communications Decency Act - is not responsible for the content it publishes.

"Sites that are seemingly well intended are turning into wastelands of defamatory and unspecified allegations," said Aaron Morris, a partner with Morris & Stone LLP in Orange County who is not involved in the case. "There needs to be some sort of blowback against unfettered speech. People should be able to go on and say, 'That's not a true statement about me, and I need to be able to attack this.' "

Norberg, who has a day job designing furniture, had no complaints about his medical care - only how much he was billed for it. In his original review, he wrote, "I don't think good business means charging people whatever you feel like hoping they'll pay without a fuss."

About two weeks later, Biegel wrote to Norberg saying that he was "saddened" by the review and that Norberg misunderstood standard medical billing procedures. Biegel said he asked Norberg to reconsider or remove the review.

"I did not do anything unethical or illegal in our entire dealings," the chiropractor said.

Instead, after receiving a cease-and-desist letter from Biegel's lawyer, Norberg replaced the review with a second posting that remains online.

Biegel's business has been hurt by the reviews, said his attorney, Eric Nordskog of San Francisco. "Although negative reviews are fine, there are certain statements that are false statements of fact," he said. "He accuses Biegel of dishonesty and of committing insurance fraud, which is a crime in California."

Norberg's attorney, Michael Blacksburg, called the reviews "opinion statements" and said that Biegel's business fell off after he filed the lawsuit because the number of referrals he got from Yelp dropped.

"Customers who use Yelp don't want to be another potential lawsuit defendant if they choose to write a negative review," Blacksburg said. "It has nothing to do with who's right or wrong - they're going to go with the chiropractor who chooses not to sue."

The Electronic Frontier Foundation, a local nonprofit that supports free speech online, is considering helping with Norberg's defense. Matt Zimmerman, an attorney with the group, said Biegel will get far more negative publicity from filing the lawsuit than from a bad review on Yelp. He said the foundation is seeing more and more cases of people trying to use the courts because they're unhappy with postings on the Internet.

"When people try to pull down unflattering material, it has the absolute opposite effect" of what they intend, he said. "It's very difficult to silence speakers on the Internet - it's a culture of people who don't like those kinds of attempts."

Stephanie Ichinose, a spokeswoman for Yelp, agreed. "Suing one of his patients over a single review (in light of the many positive reviews that he receives on our site) might end up tarnishing Dr. Biegel's reputation rather than enhancing it, not to mention the costs associated with litigation," she said in an e-mail.

Ichinose added that the site tried to head off the lawsuit by mediating the dispute because "both brought legitimate concerns to the table."

Meanwhile, Norberg has started a Web site, standforspeech.com, which has been visited by more than 2,500 people, as well as pages on Facebook and MySpace to raise money for his defense.

"I regret leaving myself so wide open," he said. "I might have taken a couple of days to think about what I could say, but it's Yelp. I experience something, go home and write about it while it's fresh in my mind, then I don't think about it again. If I waited a couple of days, I might not have put anything up."